What if Weaver’s Changeup is the Problem?

Fear, confusion, and hope. If you have watched any of Luke Weaver’s seven starts this season, you’ve battled each of these feelings. Sometimes together, sometimes apart, the product of 35 ¹⁄₃ innings blends each into a cocktail of emotion, with fans in search of solace to ease the pain.

While feelings around Weaver can be complex, understanding his approach is relatively simple. At his core, the righty is largely fastball-changeup dominant with increased overall usage in his curveball compared to 2017 and the fleeting look at a cutter that can easily go unnoticed.

His mix to right-handed hitters has remained largely similar compared to 2017, with more noticeable tweaks coming to lefties, the handedness of hitter that he was able to neutralize effectively last season. This is where you see a nine percent jump in curveball usage and brake pumping on his changeup (down five percent).

Given that most changeup-dominant righties possess these reverse splits (like Weaver, better versus lefties last year), after seeing the difference in Weaver’s effectiveness to both sides of the plate year over year, our old friend confusion remerges.

One might suspect a right-hander with a great changeup that suddenly has trouble setting down left-handed hitters experienced some change in the very pitch responsible for this issue. Fangraphs “pitch value” metric confirms Weaver’s changeup has been relatively neutral in a small sample, but results only tell us so much if we want to set expectations for further adjustment back to natural results.

While likely invisible to the naked eye, Weaver’s changeup has altered its shape compared to 2017.

Weaver’s changeup lacks the same vertical depth this season, but has picked up more arm-side run away from left-handers and in to right-handers. This appears to have made the pitch easier for hitters to square up, resulting in boosts to opponent isolated power and slugging against after a season where the pitch wasn’t hit out of the park. But I hesitate to confirm a correlation between this subtle change in movement and notable differences in results, given, for instance, that Weaver’s location of the pitch remains suitably at the knees and its whiff rate remains stable.

Changeups themselves are fickle pitches and often necessitate adventures into pitch tunneling. The concept has been modified by Baseball Prospectus (BP) in the past year, but a few of the data points remain relatively intuitive: release distance (self-explanatory), pre-tunnel max, and pre-max ratio. (The latter two are named to terrify even the most seasoned baseball analyst.)

Pre-tunnel max is simply the distance of a pitch sequence form each-other at the hitter’s decision making point (let’s call this “tunnel distance”). Pre-max ratio is how much of a pitcher’s distance in the plate location of two pitches comes from movement at the hitter’s decision making point (“late break” relative to another pitch).

One of the larger changes to how tunneling was calculated relates to splitting the tunnel data based on the handedness of hitter, based off the logic that tunneling is tied to perception and a right-handed hitter would perceive Weaver’s changeup different from a left-handed hitter.

This is where an interesting data point reveals itself.

Weaver’s most used, non-fastball-fastball combination of pitches is predictably his fastball-change and mentioned above is Weaver’s flip-flopping in effectiveness versus left-handed hitters. What if Weaver’s not tunneling his fastball-changeup combo as well to that side of the plate?

This isn’t the holy grail of pitch statistics, but the concept can get one really thinking about how a game is called and how pitches play off each other. Most important, we have some information that suggests pitches closer together at the hitter’s decision point and subsequently further away at the plate, leads to more swinging strikes, but as we also know, the concept of tunneling itself is still somewhat etherial. Pitching will never stop being an interpretable art.

Something might be off with Weaver’s changeup, but should the results really be this rocky given only slight variations on what is still a pitch generating a decent amount of whiffs?

That led me to think about Weaver’s curveball, a pitch chronicled recently by VEB’s Tyler Kinzy. Two things mentioned in Tyler’s column stand out.

First is the improvements Weaver has made to the pitch, generating both more velocity and horizontal break, adding some slurve and bite to the pitch. Second is the qualifier that even with a harder feel and more break, the spin rate on the pitch has continually lagged behind, this year sitting in the bottom 15th percentile in the league among all curveballs thrown. While spin means different things for different pitches - fastball spin is meant to achieve a “rising” effect; curveball spin intends the opposite - studies support the notion that greater spin rate has some correlation to a higher chance for swing-and-miss.

Improvement is good, but while understanding Weaver’s changeup brought us from results to granular details, his curveball takes us in the other direction: from talks of bend, velocity, and spin, to output.

That output is the realization this hook has struggled to produce results in back-to-back years. It’s struggling to elicit whiffs at an average rate and is consistently one of the hardest hit balls in Weaver’s repertoire.

The notion that a curveball is needed for a two-pitch arm to provide diversity of pitches has its merits, but the gap between the Weaver we have and the Weaver we saw further development bringing us can be focused on the viability of this pitch. Calibrating Weaver’s changeup effectiveness and crossing our fingers on the development of his curveball will dictate the rest of this season for the young righty.

Weaver’s next start comes Friday night in San Diego. Keep an eye on how effective these two pitches are against one of the weaker offenses in the league. It could be the first step back onto the right path.

I can be found on Twitter - @LanceBrozdow

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